Hybrid electric vehicles selectively use an internal combustion engine as a source of input torque to a transmission, alone or in conjunction with the traction motor(s), while extended-range electric vehicles use a smaller engine only when needed, and solely to power an electric generator. Battery electric vehicles forego use of the small gas engine, and instead operate using stored electrical energy or regenerative braking energy. All three vehicle configurations can operate solely on electricity in what is referred to as an electric vehicle (EV) mode.
In some of the above vehicle embodiments, a Rechargeable Energy Storage System (RESS) is used to alternatively store and deliver the substantial amounts of electrical energy needed for driving the fraction motor(s). The RESS may consist of a battery pack having multiple battery modules each containing multiple cylindrical or flat/tabular battery cells. The battery pack generates heat in operation. Effectively dissipating the generated heat is essential to optimizing vehicle performance. As a result, thermal management systems are used in conjunction with battery packs to circulate a volume of a suitable cooling fluid through 1) the battery pack and any associated power electronics; and 2) an active heating circuit and cooling circuit to control the temperature of the passenger compartment.
In some thermal management systems, the system may operate in two operating modes, namely heating mode and cooling mode, either independently or simultaneously. During heating mode, the system employs a heat pump condenser, inside the HVAC module or within the vehicle underhood, and the RESS chiller as the heat pump evaporator. Additionally, the heating circuit may include a cabin evaporator, which may be configured to cool and dehumidify air transmitted to the passenger compartment. In cooling mode, the system utilizes an independent AC condenser outside the HVAC module, and a cabin evaporator.
In such systems, it is not necessary to require the reversal of refrigerant flow when changing operating modes. Absent the requirement to reverse the system, the position of the low-pressure side of the system, defined between one of the plurality of expansion devices and the compressor, remains constant in all operating modes reducing or eliminating the need to de-ice an outside heat exchanger in heating mode, and allowing uninterrupted heating of the passenger compartment. However, these base systems are designed to effectively operate in EV mode in mild ambient temperatures.